A New Orleans federal judge lifted the six-month moratorium on deepwater drilling imposed by President Barack Obama following the largest oil spill in U.S. history. Drilling services shares jumped on the news.

Obama temporarily halted all drilling in waters deeper than 500 feet on May 27 to give a presidential commission time to study improvements in the safety of offshore operations. More than a dozen Louisiana offshore service and supply companies sued U.S. regulators to lift the ban. The U.S. said it will appeal the decision.

U.S. District Judge Martin Feldman today granted a preliminary injunction, halting the moratorium. He also “immediately prohibited” the U.S. from enforcing the ban. Government lawyers told Feldman that ban was based on findings in a U.S. report following the sinking of the Deepwater Horizon rig off the Louisiana coast in April.

“The court is unable to divine or fathom a relationship between the findings and the immense scope of the moratorium,” Feldman said in his 22-page decision. “The blanket moratorium, with no parameters, seems to assume that because one rig failed and although no one yet fully knows why, all companies and rigs drilling new wells over 500 feet also universally present an imminent danger.”

Separate Order

“The court cannot substitute its judgment for that of the agency, but the agency must ‘cogently explain why it has exercised its discretion in a given manner,’” Feldman said, citing a previous ruling. “It has not done so.”

Feldman in a separate order today “immediately prohibited” the U.S. from enforcing the drilling moratorium, finding the offshore companies would otherwise incur “irreparable harm.”

White House press secretary Robert Gibbs said that “continuing to drill at these depths without knowing what happened does not make any sense.”

The U.S. argued that the moratorium was necessary to assure public safety.

“We need to make sure deepwater drilling is as safe as we thought it was the day before this incident,” Brian Collins, a lawyer for the government, told Feldman in a court hearing June 21. “It is crucial to take the time because to fail to do so would be to gamble with the long-term future of this region.”

Biggest Quantity

BP has two pipes collecting oil and gas from the ocean floor. They collected 25,830 barrels of oil yesterday, the biggest quantity diverted from the Gulf of Mexico since the April 20 spill began, London-based BP said in a statement. BP spokesman David Nicholas declined to comment on the ruling, saying the company was not a party to the case.

Lawyers for the drilling companies told Feldman the moratorium illegally sidesteps a required industry comment period. They also said regulators failed to tell Obama that all active deepwater rigs passed an immediate re-inspection after the Deepwater Horizon exploded and sank, with only two rigs reporting minor violations and the rest getting approval to continue operations.

Henry Dart, special counsel for the Louisiana attorney general, told Feldman that federal regulators failed to consult with state officials about the impact of the drilling ban, allegedly violating U.S. law.

Jobs in Danger

“Even after the catastrophic events of Sept. 11, the government only shut down the airlines for three days,” Louisiana said in court papers seeking to lift the ban.

Lawyers for the state and oilfield companies told Feldman that the ban could cost as many as 20,000 jobs if the moratorium lasted 18 months.

“The defendants trivialize such losses by characterizing them as merely a small percentage of the drilling rigs affected, but it does not follow that this will somehow reduce the convincing harm suffered,” Feldman said. He said the economic impacts of the ban would “clearly ripple throughout the economy of this region.”

Feldman granted the injunction after finding it likely the oilfield companies will succeed in proving “the agency’s decision was arbitrary and capricious,” which violates federal law governing policy decisions.

‘Immeasurable’ Effect

“An invalid agency decision to suspend drilling of wells in depths over 500 feet simply cannot justify the immeasurable effect on the plaintiffs, the local economy, the Gulf region, and the critical present-day aspect of the availability of domestic energy in the country,” Feldman said.

“Today’s ruling by U.S. District Court Judge Martin Feldman is an important step in returning thousands of oil service workers to their jobs,” Royal Dutch Shell Plc spokesman Bill Tanner said in an e-mailed statement.

“Shell remains confident in its expertise and procedures to safely drill and complete deepwater wells.” Shell’s safety standards often exceed regulatory requirements and include including a rigorous training program for well engineers, Tanner said.

Realistically, not a lot has changed, said Jud Bailey, an analyst at Jefferies & Co. in Houston.

“It’s a small victory for the industry, but clearly the administration has dug in its heels and is going to try to keep this moratorium, come hell or high water,” Bailey said today in a telephone interview. “Investors, as it relates to the drillers, are for the most part staying away. There’s too much uncertainty, too much headline risk.”

Bailey said he doesn’t think many operators would run out and immediately try to resume operations. “You run the risk of this getting overturned by the appellate court,” he said.

The case is Hornbeck Offshore Services LLC v. Salazar, 2:10-cv-01663, U.S. District Court, Eastern District of Louisiana (New Orleans).